This invention relates generally to diffusion bonding and brazing of materials and more specifically to a method of establishing a physical bond between the faying surfaces of joined components such as honeycomb core sandwich panels having either a planar or non-planar configuration.
Diffusion bonding and brazing methods for the cladding of objects of various shapes and for the joining of honeycomb sandwich panel structures have hereinbefore been known and separately used with some degree of success but have not been found to be entirely satisfactory. One method used includes placing a plurality of metal members in juxtaposed intimate contact, sealing the edges thereof normally by welding, submerging the composite structure in a molten salt bath of predetermined characteristics, and applying an external high gas pressure to the salt bath which in turn bonds the members together uniformly throughout. A second method used provides for cladding by means of hydrostatic pressure applied to heated units inside a cold-liquid cladding apparatus of either the oil type or water type.
When diffusion bonding and brazing such material or titanium and titanium alloys, even greater care must be taken to insure that the faying surfaces are maintained free of contaminants. Also, conventional methods of diffusion bonding and brazing are often impractical, especially when applied to honeycomb sandwich panel structures. One method of diffusion used in the past with tubular honeycomb panels consists of depositing a laminate of diffusion bridge material on the core edges and positioning together the faying surfaces of the facing sheets and core. Next, a mandrel is inserted into the interior of the tubular assembly and a molybdenum metal mesh is wound securely around the entire outer surface of the tubular assembly with the mesh being tack welded to the underlaying wrap to hold it in place much in the manner of a girdle. The reason for the mesh is that when titanium is heated to the 1700.degree. F. range, it becomes soft with drooping occurring due to its own weight and a restraining structure is necessary to insure good pressure at the faying surfaces while the diffusion bonding is occurring. A major drawback to this method is the fact that the molybdenum mesh become brittle during repeated usage and can normally only be used about four times. This, added to the fact that the mesh is expensive, has made it desirable to look for an alternative method that would eliminate the need for the mesh, thereby saving several hundred dollars per unit to be diffusion bonded on a normal jet engine housing duct.